Process of refining graphite



such asiron, aluminum, copper and so forth.

Patented 27, 1935 PnocEss' or Absalom M.

Kennedy, University, Ala., assign01- xto W. H. Weller, Jr.

No Application April 2 1,t 1 s 4,fseria1 1 j 1 ,HT'NQQZ J G .f 3 Claims: (olozszas).

, This application is a substitute for my pre viously filedapplication, Serial No. 339,283, filed Februaryll, 1929. p

invention relates to the refining of graphite after it has been concentrated from natural graphite ores and has for its object the simple and economical production of graphite containing a very low; percentage of metallic impurities,

' A furtherobject is to'provide a process for the production of refined graphite, utilizing therein an-acid reagent-to remove the metallic impurities and to regenerate this reagent in each cycle of operation of the process. p

1 A still jfurtherobject of this invention is to provide a process whereby a highly refined;

graphite suitable foruse in theLeclanche type of dry batteries is produced from relatively low M gradjefor graphite ores;

' Theuse of graphite together with manganese dioxide as a material" for the positive elementsot drybatteries is rapidly increasing. For such use; silica, as an impurity in the graphite; is of less importance than iron, aluminum, copper, arsenic, nickel; cobalt,-etc., since these metals tend to unite with theelectrolyteandin this way to'interfere-witlrthe electrochemical-reaction within the cell; the efiect of which is to reduce the capacity of the cell and to shorten its life. I

I have found that the major part of the iron, aluminum, copper, nickel, and other metals which occur as impurities in the graphite, may be removed by treating the material with an ammonium sulphate, which reagent is regenerated in .each cycle of operation of the process, as follows:

The concentrate, which is produced by mechanical treatment of graphite ores, is digested with a solution of ammonium bisulphate.

A reaction occurs in which the metallic impurities are removed from the graphite as soluble sulphates; which reaction, letting A1203 represent these metallic impurities and C, the

graphite, which is precipitated, may be represented as'followsz The precipitate is separated from the solution and is washed and dried.

To the solution is added ammonia, as that pro- The precipitate of metallic hydroxides is separated from the solution of ammonium sulphates which latter is evaporated and the resultant crystals are heatedto about 3005 0. when amformed:

f This ammonium bi's ul'phate, may be used with afresh batch of graphite'con'centrate, as inthe first reaction, thus using and regenerating this reagent in each' cycle 'offo'peration of the process. The ammonia may also, be recovered and -reemployed in the process as described above. r e

As an alternate procedure, I findthat Inlay operatewith the same materials as follows: I

The graphite concentrate'is heated to 300-,400 C. withammonium sulphate in' a closed container.

1 On heating ammonium sulphate, (NI-102804, to this temperature, one half of its ammonia content is driven off and a mobile liquid; ammonium bisulphate, (NH4HSG4) is formed which reacts with .the metallic. impurities, liberatingthe re mainder. of "its ammonia content and forming sulphates of the metals. J ,J

Water is added to the product, preferably while still hot, to dissolve out the soluble,su1phates. The precipitate is separated from the solution and is washed and dried. i

To the filtrate, ammonia, as that driven off in the above reactions, is added. This may conveniently be done by sending it through the solution. The aluminum and other metallic constituents of the-soluble sulphates areprecipitated as hydroxides. the solution.

1 agent in each cycle of operation of the process.

In practice, I prefer to operate as follows:

This precipitate is separated from The graphite containing ore is crushed and is concentrated by the usual means, as by a log washer or a classifier, so as to remove as high a percentage of the impurities as possible and the concentrate is delivered to a vessel provided with an agitator and a means for heating.

Here it is mixed with a solution of ammonium bisulphate, as that produced in a later operation, containing at least twice as many S04 radicals as are indicated to form sulphates with the metallic impurities in the graphite concentrate.

The mixture is kept continuously agitated and is heated to boiling temperature ordinarily from amount of the impurities present in the graphite The filtrate and the precipitated graphite. from the reaction described above are separated, as by a'continuous suction filter, and the graphite; is

washed, preferably on the filter, until practically free from sulphates. It is then removed from the filter and is dried; pulverized, if desired, and,

' ".rating the impurities from the solution as hyis packed. g

The filtrate, together with thatportion of the wash water containing a sumcient amount of ammonium sulphate to make the recovery economical, is collected. Ammonia, as that driven off in the reactionin which ammonium sulphate is heated "to convertfit intoammonium bisulphate,

ferred to a'closedcontainer arranged for the col lection of the gases givenlofi' and the mass'is heated to about 300 C. r

"Theammonia evolved is, collected for utilization in the precipitation of'the metallic hydroxides, as shown above. The ammonium bisulphate produced is preferably runby gravity while in a fluid state that is above 150 C., into the water for thetreatment of a fresh batch of graphite concentrate.

.While I have described my invention in but two 4 forms, it will be obvious tothoseirskilled in the art that it is notso limited, but is susceptible of various, other changes and modifications, without placedthereuponas are imposed by the prior art 15 to 45 minutes according to the nature and or as are specifically set forth in the appended claims.

What I claim is: 1.;A cyclic process of obtaining purified graphite from concentrated graphite ore containing metallic impurities, which consists in digesting .the concentrated ore with a solution of ammonium bisulphate to precipitate the purified graphite and to form sulphated impurities in solution,

separating and drying the purified graphite, sepadroxides by adding-ammonia to the solution, and

heating the ammonium sulphate formed to a temperature of about 300 C. to separate ammonia and ammonium bisulphate for reuse in the process.

2. A cyclic process of refining concentrated graphite ores containing iron, aluminum and other metallicimpurities which comprises digest ing the graphite concentrate with a solution of ammonium bisulphate, separating the graphite from the solution of sulphates, adding ammonia to precipitate the impurities as hydroxides and separating this precipitate from the solution, evaporating the solution to form ammonium sulphate crystals, and heating these crystals to produce ammonium bisulphate and ammonia for reuse with fresh conc'entrateI I 3. A process of purifying graphite ore concentrates containing metallic impurities comprising heating a mixture of the concentrates with ammonium sulphate to form a; reactive mixture of concentrates and ammoniumbisulphate and thus forming soluble metallic sulphates, adding water to dissolve the sulphates an d to separate purified graphite, recovering .theammonia drivenoff by the heat, and bringing about a reaction between the ammonia and thesolution of metallic sul phates to precipitate metallic hydroxides and form ammonium sulphate for reusewith a subsequent batch. g

' a ABSALOM M. KENNEDY. 

